The most lasting achievement of Innocent III's pontificate is his recognition of a new movement within the western church. The monasteries have shown an incorrigible tendency to accumulate wealth. In 1210 and 1215 the pope receives in Rome two visionaries with a strikingly different concept of how to follow the example of Christ.

The first visit is from Francis of Assisi and eleven of his companions. They are laymen who have given up their worldly possessions. They want to live among the poor, particularly in the rapidly growing towns, preaching and bearing witness to a Christian life. The pope encourages them.

Five years later Innocent's visitor is a Spaniard, Dominic de Guzman, who has much experience of preaching (to the Cathars) and a specific interest in correcting doctrinal error. Like Francis, he and his fellows have embraced poverty. They work amid the bustle and argument of the towns. They too are given Innocent's blessing.

From these encounters are born the two great orders of mendicant (or begging) friars, the Franciscans and the Dominicans. Western monasticism rediscovers a truth more often remembered in the east, in Hinduism and Buddhism - that the holy man's only possession is his begging bowl. But neither mendicant order, growing in power, will find the ideal of poverty easy.

The formal foundation of each order falls within the pontificate of Innocent's successor, Honorius III. He establishes the Dominicans in 1216 and the Franciscans in 1223.

This papal foundation distinguishes the friars from the more independent monastic orders, established in earlier centuries when the papacy was able to exercise only a relatively loose control. The two mendicant orders are seen and are used as an instrument of papal policy. They will be joined in this respect, after the crisis of the Reformation, by a third and even more powerful order - that of the Jesuits (who differ from the Dominicans and the Franciscans in not sharing their ideological devotion to poverty).

Dominicans: from1216

St Dominic discovers his personal mission in preaching to the Cathars in and around Toulouse from 1206. The heretics of this region remain the first focus of the Dominican order after their official establishment in 1216. The Latin name given to the order by the pope reflects their central purpose - Ordo Fratrum Praedicatorum, Order of the Friars Preachers.

In Toulouse in 1219 the friars adopt the dress which gives them their more familiar name. They wear a white woollen tunic and hood for everyday use, and above it on more formal occasions a black mantle. They become the Black Friars.

From the start Dominic demands high intellectual standards from his friars. As early as 1218 he sends some of them to study and preach at the university of Paris, and two years later sends others to Oxford. By 1248 special hostels for Dominican friars have been established in the university towns of Paris, Oxford, Cologne, Monptellier and Bologna.

The intellectual leaning of the Dominicans is soon matched by the other order of mendicant friars, the Franciscans - though their first concern, in keeping with their founder's example, has been with the simpler demands of piety and poverty.

From the middle of the 13th century the leading figures in scholasticism are friars of one or other order. Albertus Magnus and Thomas Aquinas are Dominicans. Bonaventura, Duns Scotus and William Ockham are Franciscans.

There is one area of Christian activity which remains primarily the preserve of the Dominicans. In a tradition going back to St Dominic among the Cathars, they specialize in the rooting out of heresy. When the Inquisition is first established on something approaching a formal basis, in 1233, the work is entrusted to Dominicans.

Franciscans: from1223

Francis, a worldly young man of Assisi and for a while a soldier, is moved in about 1205 to give up all his possessions. He devotes himself to rebuilding ruined churches and chapels with his own hands. He is joined in this task by other like-minded idealists. One restored chapel, the tiny Porziuncola, becomes their main place of worship. It now sits, like a precious relic, in the great church subsequently constructed to shelter the little building and to accomodate its numerous visitors.

The simplicity of St Francis, and his sense of one-ness with all created life, strikes an immediate chord with his contemporaries - and with all generations since.

Such is the reputation of Francis in his lifetime that he is canonized in 1228, within less than two years of his death. His order of mendicant friars has spread rapidly through Italy since the first informal approval given to Francis by Innocent III in 1210. The order is formally approved in 1223.

A sister order for nuns, headed by St Clare, is founded at Assisi in 1212 under the aegis of St Francis. The status of the Poor Clares as the second Franciscan order is authorized just two days before Clare's death, in 1253, when the pope allows them to follow Francis's rule of 'perfect poverty' rather than the rule of St Benedict.

Perfect poverty proves an unattainable ideal even for the mendicant friars following the example of St Francis. The Latin name given to their order (Ordo Fratrum Minorum, Order of the Friars Minor) emphasizes that humility is supposed to be their main characteristic - just as preaching is that of the Dominicans.

But within twenty years of St Francis's death a Franciscan, Odo Rigaud, is archbishop of Rouen, with three palaces and massive estates. When he is riding to Rome with a retinue of eighty horsemen, an Italian bishop offers to pay his expenses. Odo replies, with devastating honesty but not in the spirit of St Francis, that he has no need of charity.

The issue of poverty splits the Franciscan order into two camps, the Spirituals and the less strict Conventuals. The drift of late medieval history is on the side of the Conventuals. In 1322 the pope even condemns as heretical the doctrine of the poverty of Christ. A fat friar becomes a familiar figure of satire; 'wanton and merry' is Chaucer's thumbnail sketch of the friar among the Canterbury pilgrims.

Yet, whatever their faults, the Franciscan and Dominican friars meet the needs of the urban culture of the late middle ages as effectively as the monks in the great monasteries fulfilled the requirements of earlier centuries.

Augustinians: from1256

The Dominicans and Franciscans are joined, from 1256, by the third great order of preaching friars. In this year the pope, Alexander IV, gathers together into a new mendicant order several groups of hermits who are living in north Italy and are following a monastic rule believed to have been written by St Augustine. The pope directs the Augustinians to undertake missionary and educational work in the developing cities.

Soon, like the other friars, they spread throughout Europe (the most famous but disobedient member of the order is Martin Luther). And they are prominent in the great expansion of missionary activity in the 16th century, to India and the far east and to Latin America.

Rival missions: 16th - 18th century

In the great period of Roman Catholic missions, during the Catholic Reformation, the Spanish and Portuguese expansion round the globe is everywhere accompanied by members of the four great preaching orders - Dominicans, Franciscans, Augustinians and Jesuits. The Jesuits, starting later and moving faster, are the most energetic. By 1615, at the end of the long generalship of Claudio Aquaviva, they have divided the world into thirty-two provinces in which they run more than 200 colleges.

But the success of the Jesuits, together with underlying differences of attitude, provokes the hostility of the Franciscans and Dominicans.

There is a deep distinction, in their origins, between the two older orders and the newcomers. The Franciscans, in particular, were established to live and preach among the poor of the cities. The Jesuits, special agents of the pope, are better adapted to moving among people of influence.

Tensions between the groups partly cause the disaster which strikes the Christians of Japan, where the Jesuits convert the nobility but the friars devote themselves to the poor. The Japanese, appalled at this dissent among Christians, persecute and ban the religion.

In China a similar development occurs. The Jesuits, under the leadership of Matteo Ricci, integrate so well with the hierarchy that they allow their converts to engage in Confucian rituals - arguing that these are social rather than religious. The Franciscans and Dominicans disagree. They take the issue to Rome, where it becomes known as the Rites Controversy.

As in Japan, these signs of dissent among Christians disenchant the Chinese. In the early 18th century the Kangxi emperor, noting disagreements between the orders and even between Portuguese and French Jesuits, observes that 'this violates the principles of religion'. Meanwhile even in Europe there is increasing criticism of the religious orders during the 18th century.

All three orders lose prestige in the anti-clerical mood of the Enlightenment. But it is the Jesuits, with the highest profile, who attract the greatest hostility. Between 1759 and 1761 Portugal arrests all the Jesuits in its territories and ships them to the papal states. In 1761-3 the Jesuit colleges in France are closed. In 1767 Jesuits are expelled from Spain and its colonies.

For a few years Rome resists mounting pressure to abolish the Society of Jesus altogether, but eventually Clement XIV succumbs in 1773. In the very different mood at the end of the Napoleonic wars, Pius VII reinstates the order in 1814.

Monks, nuns and friars in the modern world

The prestige of the religious orders suffers almost fatally from the anti-clerical spirit of the late 18th century (culminating in the suppression of the Jesuits), and from violent hostility during the French Revolution. Monasteries, even in Catholic countries, never again recover the economic power which they once enjoyed. And the preaching orders lose much of the influence acquired during the fervour of the Catholic Reformation.

Nevertheless the 19th century sees a strong return to a more religious mood in society, and to a romantic rediscovery of the great Christian centuries of the Middle Ages when monasticism was at its peak.